Radio compass



Aug. 24, 1943. F. J. HOOV-EN RADIO COMPASS Filed Feb. 12, 1936 5 Sheets-Sheet 1 IN V EN TOR. 51 62 67? 2} CI 15 000672 BY 6 Okla ATTORNEY Aug. 24, 1943. F. J. HOOVEN 2,327,641

RADIO COMPASS Filed Feb. 12, 1936 3 Sheets-Sheet 2 I: viz-E A; (@840, fwd

8 IF; Ira- 5 INVENTOR. flearzi'djyaaa'iz ATTORNEY Aug. 24, 1943. F. J. HOOVEN 2,

RADIO COMPASS.

5 Sheets-Sheet 3 Filed Feb. 12, 1936 A MP1 #75 HATFA Riff/VIA Mapw A 70/ INVENTOR.

ATTORNEY Patented Aug. 24, 1943 a v I ahnio COMPASS I .lFrederick Ji 7 Hooven, Dayton;- Ohio, assigncr to t .v

tRadiotCorporation of America, New York, N Y., a corporation of Delaware 7 c Application FebruarylZ, icsaseri im eases r2 claims; (oi. wai 11i 1 f My invention relates broadly to-radio-corn= passes" and more particularly to a" circuit-ar rang'ement for a compositevisual and-aural radiocoinpa'ss system,

One or the objects or my i vention is-to' brovide a construction o'fradio' compass of high precision having means for combining signalingem ergy received both'non-dire'ctively and directive ly and controlling the operation of a visual indicator for precision operationindependently of the amplitude of the received signaling energy. 2

Another object of invention is to provide,

a circuit arrangement for' a radio compass hav: ing means for controlling the bias potential on certain of the circuits of the amplifier system which connects with thedirectional antenna for insuring precision operation of a visual-indicator regardless of the amplitude of incoming sig naling energy incident upon the directional an-y tenna relative to a nondirectionalaritennavasso;

ciated with the radio compassl Still another object of m invention isto pro-y vide a circuitarrangement tor-a radio. compass in which an amplifier connected in cir'cuitfwith a directional antenna is compactly assembled with an oscillator and a receiving system connected Another'olojectof mydnven'tio'nistoproiiid a: circuit; arrangement whereby the characteris ticsofthe circuit'are-independerit ofthe imped 5 ance of' the attached indicators, permitting-sh free interchangeability of indicators oritlieus'eiof a plurality of indicators without disturbing' the operation of, the radio'coriipass, 3 A further object of my invention is to-providea circuit arrangement whereby a tuned 'non-di rectional antenna maybe sued withoutpossibility of erroneous indication due to" possible :nis

tuning of the non-directio nal antenna-system." Astill furtherobjectof my in'ventioniis to 1 "provide a radio compas'sc'ircuit which may he adapted-torunction as I an ordinary *recfeiver by. i means oia's'imple switch.

- Anotherobject :orm vemmh is to want i circuit which makes possible'the' use of a trans;

mission=-lineconnection to' the loop antenna with" @theloo'p antenna-"remote from'the remainder bii ";the' system. 1

Other and further objectsof myinventionura L v 3 sidein the"circuit arrangement -for a radio;corn-.

25* c i t i panymg. drawings, in which:

- Figure Lis-a diagrammatic andsch maticg vi with a non-directional antenna andiclo'selyv assoi ciated. with a visual indicator andcontrolrmech' anism' associated therewith with means rdhavhiag ing any detrimental effects due to variations in potential which may. occur in one portion" the apparatus from being impressed upon any other portion of the apparatus. I

Alfurther object of myinvention isto provide,

a circuit arrangement for a radio compass'l in which a visual indicator device has the actuating windings thereof electronically coupled with the-actuating circuits oi the-radio-compassso that the characteristics of the actuating circuitsare not afi'ected by the characteristics of the my invention is to showing the circuitarrangement foritheivisual and aural .r'adio compass of rmy inventi'omi- Referring toj i 'ig il of the drawinggj-the compass includes the shieldedloep l connected', (ff

pass as set forth more ful-ly'in the specification hereinafter following by reference tothe acco 2,- 3, 4, and 5 are polar,and"vectorialidiagrams illustrating:the principles or operation [-of system-of1my invention ;-l Fig. 6; is a schem view illustrative of asimplified circuit-of the sys tem'of my, invention; andFig. 7*is-a schematic-f View showing the adaptability or my -invent for operating two-or moreindicators on; a craft-l a a through shieldedconduit 2 to the input systemj of the receiving circuit shown generally; at 3.

I provide a novel means of connecting 'loo'p- I with the input system by whichian, increaselin' radiomfrequen'cy potential is efiected .hy: means Pof the aura transformer couplingsystemitrafi'liey inductance 5*0'f: the auto transformerfl'coiipiing. V

system has. the opposite' endsrthereofconnected 'vide acircuit arrangement for increasingth'e radio frequency potential applied to an amplifier system from a directive antenna for insuring the precision operation of an indicator controlled by the amplifier system. 7'

A further objector my invention isztolprovide I The shield 2 for the leads.

an electronic switch system for a balanced mode ulator circuit in a radio compass receiver having means for alternately rendering differentpaths through the balancedmodulator system effective. 5'.

throughcouplingcondensers 6 and! toi the con? trol grids 8 and 9 of electron tubes I!) and II. The inductance 5 istapped at IZ'and 14 to es-Q ,tablish connections with'the leads 15 extending I from the terminal of the loopl'. The steels: which partially surrounds the conductors of the loop'l is connected to ground I! which also con- V nects to theielectrical center of the loop at il8;.

I g :15 is connectedfto ground 1! as indicated, The. electrical ce'n l9 7 1 of, inductance 5' is connected to'groundfZliwmch 1 is also. connected atthefrceivirig'set and to e onduit 2 shielding the: pace 15'. The input tem is tuned by means of variable condenser 2!. The electron tubes which I have shown embody in addition to the control electrodes heretofore described, cathodes 22 and 23, anodes .24 and 25,

' shield grids 26 and 21, modulating grids 28 and I08. The tuning condenserZl of the directional,

loop circuit is mechanically coupled with the tuning condenser 3'! in the tuned input circuit 34: as indicated by broken line 39. y

In the system of my invention, the voltage induced in coil 36 by coupling coil 38 and the volt-, ageinducedin coil 36 by non-directional antenna 32 remain in constant relation and within a vector angle of 1 45. The coupling coil 38 is connected in circuit with the'anodes 24 and 25 and in circuit with the source of potential indicated generally at 50 connected through resistor il as indicated. The resistor H coacts with condenser 42 grounded at '43 to provide a filter for preventing variations in the plate current in the tubes H3, II and 59 from impressing any degree of similar variation from the source of'potenti'al 40 upon the receiver 35,, or upon the amplifier indicated generally at I8. I have shown resistors 35 and 46 connected with modulator grids 28 and.

2-9 and serving as grid leaks for the said modulator grids. I provide resistors 41 and 48 With an intermediate connection 49 to a point intered to ground at 51 as is cathode 58 of tube 59. One end of coil 54 is connected through condenser 50 to control grid GI of tube 59, control grid 6| being connected to, ground 5'! through resistor 62. The opposite end of coil 54 is connected through condenser 63 to the shield grid of the oscillator 44 is completed through the mediate resistors 55 and connected to ground at 50. Resistor 41 serves to provide a positive voltage on cathodes Hand 23 with respect to ground which voltage isa function of the total cathode current of tubesllll and l I. This voltage provides that control grids 8 and 9 may oscillate through any normal range without becoming positive with respect to cathodes 22 and 23. Re

sistor 48 serves to determine the potential supplied to screen grids 26 and 21 through resistor 5| from the high potential supply 40.

'The oscillator 34 is capacitively coupled tothe modulator grids 2B and 29 through condensers 52 and 53 in such a fashion as to impress on modulator grids 28 and 29 audio frequency voltages of equal value and opposite phase.. The plate potential is supplied to the oscillator plate 63 through a circuit connection which includes is determined ,by the inductance M and condenser 55 but is entirely independent of the im'-' pedance connected to plate 66, the oscillatorcircuit being complete with grid 6|, cathode 58, shield grid 64, coil 54 andcondensers 55, 60 and 53. The electrical center 56'of coil 541s connectwindings of the indicating mechanism shown at 61. i

The indicating mechanism 61 comprises an electromagnetic system having pole pieces 68 and 69 between which an armature is mounted for pivotal movement, which armature carries windings 10. The armature actuate the indicator arm ll operativeover. a suitably calibrated dial l2: The electromagnetic system of the devicefi'l is provided with actuating windings 13 and 14 which are preferably tuned to the frequency by means of condenser 15 and connected in such afa'shion that the magnetic flux resulting from current flowing in coil 14 is, in the same direction as magnetic flux resulting from current flowing in coil 13. i i

The windings l3 and 14 are tuned for the reason" of improving the power factor of the circuit,

comprising coils 73. and 14 and condenser I5 providing thereby the maximum" of current in said coils with the result that thesensitivity of indi cator 61 is at a maximum. Another reason for the tuning of these coils is that the reactance characteristic of thecircuit comprising these coils and their associated condenser will not be changedby the addition of one or more similarly tuned coils to the circuit in the event that it is desired to operate morethan one indicator from the sameradio compass system. Because'of this,

the phase angles of the separate currents in a plurality of coils so connected will be the same regardless of the number of such coils connected.

The armature winding [8 is connected through leads '6 with theoutput transformer 1''! which connects in the plate circuit of amplifier tube 18.

The amplifier tube 18 connects with the output system 'of radio, compass receiver 35 through a filter system consisting of coupling condenser 19, coupling resistor 30, coil 8|, which is tuned to frequency 7 by meansof condenser 82. A tap 83 of coil 8| is connected to ground. One end of coil 8| is connected to control grid 85"ofamplifier tube 1 8, The shield grid-86 of amplifier tube 13 is connected to the other end of coil 8| through condenser}! and is supplied with apositivepotential through resistor 88 from source 40. It will be seen thatthis connection of the elements of tube 18 is such that tube but condenser 81 and resistor 88 are so proportiohed that'tube 18 is not permitted .to oscillate at frequency 1 1'8 will tendto oscillate to whichcoil 8| is tuned by condenser 82. The

zfififiiii v s I ewe wheels emit-appetitetetne piie eenl plate" potential for tube 78 1s supfilieflj ifoin' the poteiitiel seureeftn 'tii'reuen eeditt; niehg eonie; neets through the pri rs win n s bf o fi transformer 11w en c e en; The iitput s5. former is" tuned to the frequency in describing the method or went-lee oftli'e radio direction finde'i', let it be assufriieafthet triej 'i'e' oruie express on;

reeeiyer -35, the loop the-tuning Ch -"3E; ar tuned ts a frequenc 1 whose" field strength at the p mtee oeation er the'directi'on'finderisi V t: 1

' end 'whose angle with a: line mm to" th'plen'e' of'the'flo'op l is 0. Theeurre l by this field strengthi A InfFig. 2 ,'-I- have plotted the alues of thetolt ages impressed on grids 8 and 9 with respect tee else variable. r 3 I \The voltage impressed; on modulater grid la f;

and 29 may be expressed asz v i U and is of such a. valuethet during tnethelf-"er the audio lfrequeney Cyl during Wfiliibh fiibfifrlator grid. 29 18 mostii'egative 15,6 ground tube H cea'ses to function diietd' the restricting eife'ct on the (if-the time of the negative voltage-on modulator 'g rie 2'9; Di-if ing this half of the 'audi'o' fre'queny cye1e;"-tne e3 modulatorg-ridflfl is in'o's't positive and {tube-I0 will function. D'u'rihg'th other half tif Hie 9.11316 frequency cy'cl'e, .grid 28 will he mase r re'g'etwe andtube ID will 'ceasit'ofunbtionand tfibflwfll Y function: Inasmuch esthera'dio freq'u'enfei 'iroit- 7F) ages impressed on the edntrl grids! 8'. and- 901 tubes JD and H areiii.oppositeipheseiit tfifi follows that the curfent-uinhedil '38,rsey,+in tne common anode, circuit of tubes fliventl ll wili have a; phase anelerduringiai ie half; the maze Gem-win then e espre sedfby;

I." actanoeetxthelowf 'equeimy sentedin Fig. 3-from-theeq -1ation:

- The resultant voltage i coil 36:

oftheeiirrent uuriiig'the other belief-the studio;

fi'equeney cy'eiel eonsi-derihg' the tubes 19, and" Sm uiet I sine-e i z'ider al 1 coi-iditins,- 1'i is smen tee tee wmi ieeit. is permissmlete melee: tliefirsttenn- Samar mettteeIt in 1 Assuming that the toil 382w mtttgmgngtet where aisa phese angledeprendingi m-rthe' This; will be recogm'zedas'a Weveeimsi'stingbfl two' eidebands .er frequ nc wi'iwzqrespeetively, 7

Without a barrier; which may; also: be Written: sin asin 'ee ete 1 Ihere' is also added IO this vo-ltag e the; induced ,by the antenna-32, graphically retiree" "sin pit I By adjusting the reactances of} the combination 0i eoilsiifi and, 38 and sometimesfby detuning the loop end essoeiated cireuits I the Z an le is kept-small, The relation ,of E emd is shown-by a; ve ctor diagrem in iiigt v 4 with .the t angle -somewhet exaggerated Figzfi-shows the I resultalnt of the curvesshown' in ,7 .Eie lende' plotted with the curve shown in Fig-.2 I In-fabt, the ent re successful operation ofthe compass isdebendent on the preservation of e.

reasonably constant value for v;.the value loff' whiohjI will discuss further as thissiqecificetion proee sq, Asstininehoweven re ltneiimdment t that a; small and remains withm where the offense Will g it be apparent"that'erterpessine thro hthe redid reeiifefwhere" iti empfifled demdduift d; there will be an audio frequency Current present in the earphone ifbliiH'IUG) of l from tv'hioh'it em he observedithet "be 1,

Mii f ierity of eiidio frequen jf function of the positieii' neexpressien; the amplitude and Thisalternating potential is amplified by; tube, IBand impressed on moving'coil l vofindicatorv 61;. then, the loop deviates to theright of a line .betweenthe axis of-the loopand the received transmitter; the y direction of a the winding is such that the indicatingneedlell gtindicator.

61 willmove to the right and, similarly, if there latonas explained above, to thatnecessary to give full's'calelde'flection of the indicator, the pos- H sibility 'that.,Ee -rnay exceed, 1a. is, eliminated for all reasonable values of Es "so that the radio compass" will function properly'even' though one'of the tubes In or H"is'cornplete1y out of action.

occurs a variation to the left, the alternating potential in the output of receiver willbe of opposite phase and indicating needle cator Ii! willlmove tothe left. In order to provide bias control 1 I of indirectifier 92-in a position to rectifya portion of the output of amplifier tube 18, and usefully.

employ the rectified output to control the potential on the control grids 8; ands .oftubes I0 and I i. By means of the resistors 93 and 94 connected respectively from a cathode-pf rectifier 92 to the source of high potential and to the ground at 95, cathode 96 of rectifier 92 is .maintained at potential positive with respect to anode 91 of rectifier 92. So long as the instantaneous value of thealternating potential :communicated to plate 9! of rectifierilzthrough condenser 98 remains less than the positive potential of cathode 96 with respect to plate 91, no current flows through rectifier 92. however, that, the value of the alternatingcur rent impressed on plate S'Le ceedsthe positive.

bias of cathode 96, current flows through rectifier '92 back to ground through resistance 95! which charges condenser Iflilxthrough resistor ID! at a negativepotential'with respect to ground. This potential is impressed through resistors I32 and I03 on control grids'a and. 9, thus reducing the transconductance of ltubesrlil. and. H; and thereby serving to prevent further increase of the current in coil 38. It will'thus be seen that the bias control become efitective when the a nplitude of the signal energyfrom loop lincreases beyond a value predetermined by the *Value of the positive bias on cathode 95.

Thus, the amplitude of the audio frequency.

output of'the tube 18 impressed on moving coil 10 of the indicator 61 is limited to a vfixed pre- Immediately,

for the control grids 8, 9, of tubes- I0, and; l;I,,Iconnect,a,

My limiting system also serves to eliminate excessive interference with the normal aural reception through the earphones resulting from;

the audio frequency'tone. from the modulator.

It is apparent from the foregoing that the consistent performance of' the radio compass depends on the maintenance of the angle 0513118 phase angle between the non-directional. antenna component and the. modulator output component, at a fairly small uniform value. It is aplpparent, since the term cos 0c appears in the expressio'n for the audio output of the receiver, that or if cos :0, in no indications at all.

the features of my radio compass is a circuit a variation of .a sufiicientto cause achange in sign of cos 0: will result in erroneous indications, One of whereby a tuned antenn'a input system may be used without-risk of a .:'changeinc1this angle in the event of mistuning. The advantages of ,a tuned antenna system in the improvement of signal-to-noise ratio "at very low field strength,

especiallywith small-antennae, such-as used on aircraft, jandin improvement of .selectivityfare wellknown to thoseskilled in'the art. 1 i

It is apparent that the phase of. the voltage output of the modulator is affected by the exactness with which the loop is .tuned toresonance, and that, similarly, the phase angle of the an tenna voltage is influenced by the tuning of the antenna coil; However, it is possible to fix the characteristics of the loop and "its associated circuits at'the time of manufacture of the device;

and due to the Well known faot'that the eleclare little affected by external conditions, this determined .value necessary to give full deflection of the indicator, regardlessof the voltage picked up by loop I in excess of that necessary to pro duce such deflection. Thislimiting effect on the output of ther'nodulator' system also has other effects which are of great importance 'in 'preserving the accuracy of the radio compass in service. It was assumed above that, the tubes l0 and H wereidentical in theirelectricalcharacteristics and that the output of the balanced modulator systemof which theya're a part'would, therefore, consist of two 'sidebands' without a carrier. I I j j However, it often happens that two similar tubes become after use, dissimilar in their electrical characteristics or it is even possible that one of them might become inoperative. "In such an event, there wouldbe impressed'oncoil 36 an additional voltage of frequency'm, and'of the value? j When this'occurs, if Eu is larger than'Ea and of opposite sign, it isobvious that Eu will neutralize E and'the polarity of the audio frequency impressedfoxi indicator 5'! will be the oppositeof what it would be if E1} were-.not;present, thus causing an erroneous indication.

By limiting the output of the balanced modu+ trical characteristics of a properly shielded loop circuit will. not be appreciably affected by varying' conditions of installation; Onthe other hand, the antenna is considerably affected by external conditions and will vary through a wide range for different installationsan'd-it is necessary to adjust the antenna tuning capacity by means of condenser I09 after the installation, ismade. If this adjustment causesa phase shift in the antenna voltage without, causing a similar shift in the modulator voltage, .then the device is susceptible' to the maladjustment of possibly unskilledpersons. 1 H Y In my device, I provide. a means of 'coupling the modulator output to the tuned antennaf circuit in such a manner -thatan1istuning of this circuit will shift the modulator output voltage throughthe same angleasthe antenna voltage and will also attenuate both voltages in the same degree, thus preservingthe. important phase angleandrelativeamplitudeof both components densers;

sistanee of coi 38, E2 i th a e a olt g Ca and 1 ,5 3 the capacity a d resistancecr the a tenna sys m. hil Z1 is thexequiv lent imp dance of cciiitanld i siessoei ed n neic n- In'the event'that coils 38 and 36 are inductively coupled, the condenser 188' is of such a value that the leakage inductance will be resonant at .a' frequency lower than any to which the system will tune.

It is also possible that the resonant frequencies determined by coil 38 with it inherent shunt capacity and by the leakage inductance with condenser Hi8 be higher than the tuning range of the system in which case Cg and C would be replaced by equivalent inductances.

It will be apparent that the currents flowin in impedance Z1, which we will .calliI1Ia nd 1;, respectively, those resulting from the voltages E1 and Ez, wil1 induce voltages across Z1, which will have to each other exactly the same phase angle A s the angle between h two currents, re ardless of the character or value orZi; is not resonant, its impedance'is small compared with Ca and Ce so that the currents I1 and I2 willmaintain substantially constant phaseangles with respect to E1 andliiz. The foregoing is only true considerin El andEz to have identical frequencies.

When, Z1

erally at 40. V I 7 The control switch" l 65* has? been shown'zfor cutting on and ofi the radio, compass-independently of the. operation of the nonidirectional radio receiver t5. The mannerin which the'sy'sv Dueto the sidebandspresehtin lEhthis is not precisely true, but we is always so small; compared with o1 that thediiierence in frequency-i5 .neg-' li gible. I I The value of Ce in Fig. 6 is of high impedance compared with the impedance of the system .com- I prising E2, Ta, Ca and Z1, so that when itislde sired to use the associated receiver 35 as an ordinary radio receiver, it is necessary only to interrupt the plate potential supply to the radio com.- pass system by means of switch |!1 ;5. The coupling impedance Cc being high compared with the associated circuit, the efiect of the output I circuit of the balanced modulator comprisin tubes ,lll andH and associated impedanfles in reducing the signal input to receiver {ii-from antenna 32 will be small.

If the receiver 35 is provided with automatic volume control, operated from the carrierstrength of the received signal such that the audio output voltage is proportional only to the percentage of modulation within a wide range of input voltages, then the radio compass will .provide a uniform deflection of meter 61' for a given angle of loop 5 (angle 9) within that range of input voltages, which means that if the'compassis installed on a craft approaching a. radio station, it is not necessary for the operator to compensate for the increasing signal stren th of the station as the craft approaches. This function is difierent and distinct from the automatic limiting of modulator output in accordance with audio output as described above Switch I05 serves to cut on or off the radio compass system, leaving the receiver operation. for use as a normal receiver without changing any'of the'circuits of either the receiver or compass 'Jparts'of the system, .A master control switch, not illustrated, is adapted toserve as a master control for turning off and on all power circuits to the electron tubes in the apparatus.- Telephone headset I06 permits aural reception of signalin energy simultaneously with Visual ob servation of the received signaling energy by the posit on f. in i tor en calibrated d al 1 31a 7 i rates theT rrane men or my adi om ass s hem tieallywhifch th severa units by thelo'op system upon the'ba'lancedelectron tube system the manner 0f electronically coupling the 7s infblock form wherein reference"characters ll0 designates the modulator tubes *lfland lll and i their associated'circuitsconnected with the transmission line which leads to the loop' I. Reference", character HI designates the couplingsystem whichincludes coil 38, condenser l-ll 8f,**and coil 36, 'illustrated in detail in Fig; 1.- The receiver i is indicated by reference'character 35', as in-Fig. 1, connected with antenna-32 and'with theaudible signal reproducerllifi. The block I I includes the filter constituted-by condenser 79 and resistor 80; and inductance -81, and condenser 82. The associated amplifier 181s shown asin cluded in block H4. The rectifier-tilts shown as included in block H5 connected as schematiqcallyindicat'ed with the modulator no, The oscillatorihas been shown as illustratedinFigrl, as including the multi-electrode electron' tube 59 and'associated circuits containin-ginductance I of potential is indicated em 5 1. The Source tern functions to operate two or'moreindicators is illustrated by the arrangement 'of-'the1=indica tors 61, H6 and H1. Themo ving" coils of fea'ch of the respective indicators shownrat 'lfl, Stand H Bmay be connected-in parallelto'the output? of amplifier H4. ,The actuatingwinding's 13- 74,

tors 'are shunted'by ,the tuning condensers 15;

, I24 andal 25, respectively, and 'connect'edwiththe v oscillatorj 59fas, shown. The 'condensers are-apermanent-part of the indicator structure-ssh that i.

when 'the' indicator structures are 1added=:or,.re

moved, the condensers-arei added or; removed therewith. "My-circuit is adaptable to the use of two or more indicators',"because:

a. The power factor of the circuitc'mpr-ising 1 thevarious actuatingcoils' of the indicators is unchanged by the addition or removaliof any,

combinationof coilsTana-associated condensers. 1 b. Due to theelectronic-oouplingfofthe actuating coil circuit to theoscillator circuit; the mag-{f 'nitude and characterof the impedance represented by the indicator actuatingcoil' circuit-has j a negligible efi'ecton-the amplitude and frequency of the'outputof the oscillator-1- 0. Thus, as an additional indicator separate indicators bears alike relationshipto the phase of the-voltage of-the oscillator. 3

I have indicated the connection llll whichis the plate circuit connection to the electron tube circuits of receiver+35 from the potential isource indicated at B0. IThepotential 'source'Mi is illus-l trated'asa battery butit will be understood'that a dynamotor or generator or other former-power source may be employed;

I'have found the radio compasssystem of my invention particularlyefiicient byvirtue ot-the phase control of the visual indicator, the manner s of correlating the signaling energyreceivedibyff the loop system with the signaling energyxre-.f cei-v'ed' by the antenna thernanner'ofincreasing 1 the effectiveness of the signaling. energy receive'd' f source iofj; oscillationsiwitlh thebalancedelectron illustrated in detail in Fig-,1 are shown iii-m 0s: j; 5 I iform--or the sake of brevity. That is tosay, the essential parts of the system are illustrated s llama-1, ed, it is'found that the-relative phaseof the 'sepa'rate current in the actuating 'coils of :the y the positive potential on the cathode of said rectifier, an indicator responsive to the combined outputs of said amplifier and said oscillator for indicating the relative'phase of the outputs of i said directional receivingmeans and said nondirectional receiving means;

impressing any similar degree of variation from the source of potential upon the circuitsof the radio compass receiver. These and other features of the circuit arrangement of my invention reside in the efiicient operation of the radio compass system of my invention.

While I have described my invention in'one of its preferred embodiments, I desire that, it be understood that modifications may be made and that no limitations upon my inventionare intended-other than may be imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent'of the United States is asfollow's: 1. In a radio compass systenna directional receiving means, a non-directional receiving means; an oscillator, a'modulator responsive to the combined outputs of said directional receiving means and. said oscillator, a tuned impedance coupled to said non-directional receiving means, means for coupling said impedance to the output of said modulator including means for maintaining the phase angle between the voltage induced in said impedance by, said modulator and the voltage induced insaid impedance by said nondirectional receiving -means substantially independent-of; the phase angle'betweentheresultant currentin said impedance and the resultant voltage across said impedance, a signal receiving system connected to said impedance, an-indicator responsive'to the combined-,Outputs'of saidreceivingsystem and said oscillator for-indicating the relative phase angleof the output ofsaid receiving system and the output'of' said oscillator. I 1

2. In a radio compass'system a directional receiving means, a non-directional. receiving means, an. oscillatona modulator wherein are combined the output of" said oscillator and cheer said receiving means, an impedance;wherein are combined the output of said modulator and the other or said receiving means, a receiving system for amplifying and demodulating the resultant voltage across said impedance, an amplifying system responsive principally to theffre'quency of u said oscillator andconnected ,to the output of said receiving system,'an indica-tor'having two coacting coils,*one of ,which is connected to said oscillator, the other of which is connected'to the output of saidamplifying system, and means for reducing the output of said modulator in proportion to the output of said amplifying system.

3. In a radio compass system, a directional re: ceiving means, a non-directional receiving means, an electronic modulator connected to said directional receiving means, an-oscillator connected to said modulator, a receiving system responsive to the combined outputs of said modulator and said non-directional receiving means, an amplifier connected to the output of said receiving system, a rectifier connected to the output of said amplifier, means whereby the output of said rectifier is impressed on said modulator, means whereby the cathode of said rectifier is caused to assume a positive potential with respect to the mean potential of the anode of said rectifier forreducing the output of said modulator in proportion ,to the amount by which the alternating potential onthe anode of said rectifier exceeds receiving means and said oscillator, and. means connected in the output of said amplifier and efiective on said modulatorfor reducing the, output of said modulator in proportion to the amount by which the output of said amplifier exceeds a fixed predetermined value.

5. In a radio compass system, a. directional signal'receiving system, a balanced electron tube system, connected with said directional signal receiving system, a non-directional signal receiving system, a signal receiving circuit connected with said non-directional signal receiving system, means for coupling the output circuitof said balanced electron tube system with said signal receiving circuit and maintaining the phase angle between the output voltages of said balanced electron tube system and said non-directional signal receiving system in said signal receiving circuit substantially constant, a local oscillator, means for rendering said local oscillator effective upon said balanced electron tube system, a visual indicator; and; connections from said signal receiving circuit and from said local oscillator with said visual indicator for controllingsaidvisual indicator according to theconjoint effect of the signaling energy received by said directionalreceiving system and said non-directionalreceiving system. I

6. In a radio compass system, a directional signal receiving system, a balanced electron tube system connected with said directional signal receivingsystem,a non-directional signal receiving system, a signal receiyingcircuit connected with said non-directional signal receiving system, means for coupling the output circuit of said balancedelectron tube system withsaid signal receiving circuit and maintaining the phase angle between the output voltages, of said balanced electron tube system and said non-directional signal receiving'system in said signal receiving circuit substantially constant, a local oscillator, saidbalanced electron tube systemincluding a pair of electron tubes, each containing, in addition to the operating electrodes, a modulating grid and connections between said local oscillator and saidm-odulating grids for rendering the electron tubes of said balanced electron tube system alternately efiective, a visual indicator, and a pair of coacting windings in said visual indicator, one of said windings being excitedfrom said oscillator, and the other of said windings being energized from the'output of said signal receiving circuit. u

"7. In a radio compass system, a directional signal receiving systemga balanced electron tube ,system connected with'said' directional signal receiving system, a non-directional signal receiving system, a signal receiving circuit connected with said non-directional signal receiving system, means for coupling the output circuit of said balanced electron tube system with said signal receiving circuit and maintaining the phase angle between the output Voltage of said balanced electron tube system and said non-directional signal receiving system in said signal receiving circuit substantially constant, a local oscillator, said balanced electron tube system including a pair of electron tubes, each containing in addition to the operating electrodes, a modulating grid; and connections between said local oscillator and said modulatinggrids for rendering the electron tubes of said balanced electron tube system alternately effective, a visual indicator, and a pair of coacting windings in said visual indicator, said windings being acted upon in differential phase relation by currents impressed thereon independently from the output of said signal receiving circuit and from the output ofsaid local oscillator. I

8. In a radio compass system, a directional signal receiving system, a balanced electron tube system connected with said directional signal receiving system, a non-directional signal receiving system, a signal receiving circuit connected with saidnon-directional signal receiving system, means for coupling the output of said balanced electron tube system with said signal receiving circuit, a local oscillator, means for rendering said local oscillator effective upon said 7 balanced electron tube system, a visual indicator containinga pair of windings, connections between one of said windings and the output of said oscillator, connections between the output of said signal receiving circuit and the other of said windings for difierentially controlling the operation of said visual indicator according to the phase of the currents in said windings, and means operated by energy delivered by the output of said signal receiving circuit for controlling the operation of said balanced electron tube system above a predetermined range of operation.

9. In a radio compass system, a directional signal receiving system, a balanced electrontube system connected with said directional signal receiving system, a non-directional signal receiving system, a signal receiving circuit connected with said non-directional signal receiving system, means coupling the output of said balanced electron tube system with said signal receivingcirsuit, a local oscillator, means rendering said local oscillator effective upon said balanced electron tube system, a visual indicator, an aural indicator connected with said signal receiving circuit, connections between said signal receiving circuit and said local oscillator with said' visual indicator for controlling said visual indicator according to the conjoint effect of the signaling energy received by said directional receiving system and said non-directional receiving system, and means controlled from the output of said signal receiving circuit for controlling the character-of operation of said balanced electron tube system for decreasing interference in'saidfl aural indicators by the output of said'pscillator,

connected through said balanced electrontube system.

10. Ina radio compass system, a directional receiving means, a non-directional receiving means, an oscillator, a modulator wherein are combined the output of said oscillator and one of said receiving means, an impedance, wherein fare combined the output of said modulator and the other of said receiving means, a receiving sys-' tem for amplifying and demodulating the 'resulte ant voltage across said impedance, an amplifying currents of said second carrier frequency, comsystem connected to the output of said receiving system, an indicator having two coacting coils, one of which is connected to said oscillator, the other of which is connectedto the output of said amplifying system, and means for reducingthe' output of said modulator inproportion to the output of said amplifyingsystem.

, 11'. In a'direction finder including adirective and anon-directive antenna, the methodof orienting an indicator to indicate the angular relation of a wave front and said directive antenna which comprises deriving a carrierfrequency current from said non-directive antenna,

deriving a second carrier frequency current which varies in amplitude and reverses in phase as a function of said angular relationship, ap-

plying modulationcurrents to said secondcarrier current, deriving sideband' frequency cur-- rents from said modulated carrier, eliminating bining said first carrier andsaid side band 'frequency currents, demodulating said combined "currents, deriving a controlling voltage from-said demodulated currents, and applying said c'on- 1 trolling voltage toone of said carrier currents to maintain substantiallyv constant 'percentagejof a said side band 'currentswith respect to said first carrier, currents except in the region Where said phase reverses. 1 e

12; In a radio direction finder, the combination of a directive antenna, a non-directive antenna,

a balanced. modulator eife'ctively'connected to the directive antenna, a radio receiving device,

means coupling said non-directive antenna to said device, means coupling the output of said! modulator to said device so that modulation fre- ,quency currents are applied to said device, means 'fortobtaining a demodulatedaudio output, current from said device, said output current having a frequency corresponding to said modulation frequency, and means including a rectifier re sponsive to said audio output current and connected to said device to maintain the demodulated output current substantially constant in amplitude for a given signal received for all directions excepting the regionimmediatelyadjacent the null positions offsaid directive antenna, 1

FREDERICK .J. noovE 

